A cardiac arrhythmia is a condition in which the heart's normal rhythm is disrupted. Certain types of cardiac arrhythmias, including ventricular tachycardia and atrial fibrillation, may be treated by ablation (for example, radiofrequency (RF) ablation, cryoablation, ultrasound ablation, laser ablation, microwave ablation, and the like), either endocardially or epicardially.
Procedures such as pulmonary vein isolation (PVI) and pulmonary vein antrum isolation (PVAI) are commonly used to treat atrial fibrillation. These procedures generally involve the use of a cryogenic device, such as a catheter, which is positioned at the ostium of a pulmonary vein (PV) such that any blood flow exiting the PV into the left atrium (LA) is completely blocked. Once in position, the cryogenic device may be activated for a sufficient duration to create a desired lesion within myocardial tissue at the PV-LA junction, such as a PV ostium or PV antrum. If a cryoballoon is used as the treatment element of the cryogenic device, the balloon is typically inflated using a fluid coolant, enabling an entire outer diameter of the balloon to create a circumferential lesion about the ostium and/or antrum of the PV to disrupt aberrant electrical signals exiting the PV.
The success of this procedure depends largely on the quality of the lesion(s) created during the procedure and whether the cryoballoon has completely occluded the PV. Incomplete occlusion allows blood to flow from the PV being treated, past the cryoballoon, and into the left atrium of the heart. This flow of warm blood may prevent the cryoballoon from reaching temperatures low enough to create permanent lesions in the target tissue. The creation of reversible lesions may not be sufficient to achieve electrical isolation and, as a result, atrial fibrillation may be likely to reoccur. Additionally, even if the PV is completely occluded, suboptimal operation of the cryoablation system may result in cryoballoon temperatures that are not low enough, or not applied for a sufficient amount of time, to create permanent lesions in the target tissue.
There are several ways in which lesion formation may be assessed, either during or after an ablation procedure. Such methods include imaging techniques, temperature measurement, temperature-time assessment, and cell-death models. However, each of these methods has its drawbacks. For example, standard imaging techniques may involve interrupting the ablation procedure to image the target tissue to determine if further ablation is required for sufficient lesion creation. This post-procedural medical imaging does not provide real-time lesion assessment and/or prevention of injury to non-target tissue. Further, measuring the temperature of target tissue during a procedure may be difficult or impossible, and methods that measure temperature within the cryoballoon to approximate the temperature of treated tissue may not take into account the tissue type and response to treatment, and can be very inaccurate. Likewise, temperature-time assessment methods may be based on a one-size-fits all model (for example, an Arrhenius-like equation) that does not take into account the type and depth of tissue, and may be subject to noise in the temperature data. Further, the cell-death models may not be very robust, may over- or under-estimate the effects an ablation procedure has on the target tissue, and different models may have to be used for different tissue.
It has been determined that real-time lesion formation assessment is one of the most important unmet needs for safety and efficacy of PVI using a cryoballoon catheter. None of the methods described above provides real-time temperature and occlusion feedback that can be used to assess lesion formation in real time.
Therefore, it is desirable to provide a cryoablation system and device that allows for the real-time lesion formation assessment by providing real-time temperature and occlusion feedback during a cryoablation procedure.